The present invention concerns prevulcanized treads used, in particular, for the recapping of tires. It also concerns a method of manufacturing such treads as well as an apparatus capable of the continuous production of such treads.
When prevulcanized treads are used for recapping pneumatic tires, they are either treads prepared in flat strips of long length or treads prepared in the form of rings. The flat strips by definition have an infinite radius of curvature in their longitudinal direction. In general they are without wings at their side ends which will cover the sidewalls of the recapped tires or else are provided with only very small wings. This process is known as "top-cap" recapping, since it concerns only the crown of the tire.
It is well known that when a flat tread without wings or with very small wings is used to recap tires, the lateral zones of the tread are the seat of substantial stresses; it is necessary to exert large pressures on these lateral zones in order to apply them securely onto the carcass of the tire. With this method it is practically impossible to obtain recapped tires which have the appearance of new tires. Furthermore, starting points of separation are frequently noted in the lateral zones. Federal Republic of Germany Patent Application No. 26 42 990 shows an example of a tread produced in long length.
When the tread is prepared in the form of a ring, it generally has a radius of curvature in its transverse direction so that it may securely fit the crown of the tire, as well as wings which apply themselves rather low on the shoulder, which makes it possible to obtain recapped tires without irregularity or defect in appearance. This process is usually referred to as "full-cap" recapping. U.S. Pat. No. 3,815,651 shows an example of a tread produced as a ring.
The major drawback of recapping with a tread which has been prepared as a ring is that it is necessary to use a ring corresponding to the carcass to be recapped for each size of tire to be recapped. It is therefore necessary to maintain a large stock of ring treads of different dimensions.